The invention is related to machines which are or include electromagnetically driven pumps or compressors (hereinafter for brevity termed "pump") for fluids, in which an electric rotating armature forms in effect a single rotating unit with the pump impeller or runner and is borne by a frusto-spherical surface and wherein the armature is separated from the electric motor stator by a magnetically permeable fluid-tight wall located in the space usually called the "air gap" (though we are not concerned here with air as such).
In some such machines the pump may be driven by a rotating concave pole ring (or "field") of permanent magnetic material, arranged outside the wall and itself driven by a separate source such as an electric motor or other mechanical drive source: in such case, the two relatively rotatable magnetic elements constitute a coupling rather than a motor; and in the following the terms "motor" and "coupling" are when contextually appropriate, regarded as including both.
The rotary unit or assembly of such machines is subject to axial magnetic forces, i.e. to axial thrust in one sense of direction.
Pumps in such machines are usually such that the impeller is subject to hydraulic force (the term includes fluid force) which is opposed in sense to the magnetic force thrust above mentioned. At high delivery pressures the impeller, and therefore the rotating unit of which it is a part, is subject to a hydraulic thrust towards the intake side or "eye" of the pump casing. If this hydraulic thrust exceeds the magnetic thrust force above mentioned, then the known bearing arrangement consisting of complementary concave and convex frusto-spherical components is no longer effective. This results in a design limitation in such machines.
The present invention seeks to avoid such limitation making it practicable to construct pumps particularly those intended for larger output and maybe those wherein a high fluid pressure is generated.
A further drawback of previously proposed pumps is their sensitivity to contamination of the pumped fluid especially if such contamination includes magnetically responsive particles. Contaminant particles are apt to be deposited in the "air gap".
In order to avoid these drawbacks the invention provides that a second wall, which is stationarily mounted between the armature and the impeller, is provided with a seal affording rotational freedom which seal includes part of the frusto-spherical surface of the bearing and is resiliently loaded by the wall itself or resilient means carried by the wall.